Different VE inverters in series for split phase?

Bit of a rabbit hole I've fallen down this week — anyone actually tried running two mismatched Victron units in a split-phase arrangement, specifically different wattage ratings?

I've got a Multiplus-II 3000 sitting in my cabin build and a spare Phoenix 2000 gathering dust in the van, and I'm half-tempted to lash them together rather than sell the Phoenix on eBay for a tenner.

Victron's own docs are pretty clear on parallel config needing matched units, but split-phase feels like a different beast — you're not really asking them to share load symmetrically in the same way, are you? Theoretically the 180° phase offset is doing the heavy lifting, not load balancing between identical units.

Key questions I can't find answered anywhere:

• Does VE.Bus firmware actually reject the handshake if the unit IDs don't match?
• Will the sync signal hold stable under asymmetric loads across the two legs?
• Anyone tried this with a VE.Configure workaround or custom assistant?

In practice I suspect Victron's answer is simply "buy another Multiplus, peasant," but I'd rather hear from someone who's actually smoked a fuse finding out empirically.

Worth noting this is mostly academic for a 3-phase UK grid-tie situation anyway — most of us off-grid lot are running single-phase 230V like sensible people — but for a large cabin or outbuilding with big motor loads it's a genuinely useful topology.

Anyone on here actually done this, or know someone who has? Happy to be told I'm daft.

@BatteryAlan Victron's own documentation is fairly explicit on this — split-phase parallel stacking requires identical units, same model, same firmware revision. The phase master/slave configuration via VE.Bus relies on synchronised switching logic that simply isn't designed to accommodate differing VA ratings or transformer characteristics.

Practically speaking, even if you bodged something together electrically, the VE.Bus comms would likely throw configuration errors during setup or behave unpredictably under asymmetric loading.

On my narrowboat I run two identical Multiplus-II 3000s in parallel (single phase, not split), and even there Victron strongly recommends matched firmware. Firmware drift between units causes real headaches.

If your loads genuinely require different phase capacities, the correct approach is two separate single-phase systems with a transfer switch arrangement — not a mismatched split-phase stack. What's the actual load distribution you're trying to solve?

@BatteryAlan I went down this exact rabbit hole when I was trying to cobble together a shore power setup on the boat. The short answer from painful experience — Victron's VE.Bus stack doesn't play nicely with mismatched wattages even when you think you've configured it correctly in VEConfigure. The units negotiate load sharing based on identical capacity assumptions, so the smaller unit ends up being flogged whilst the larger one loafs about.

What I ended up doing was running two separate single-phase systems and using a transfer switch to route loads appropriately rather than trying to force a proper split-phase arrangement. Messier in the locker, but rock solid in practice.

If you're absolutely set on split-phase, Victron's own compatibility matrix is worth printing out — matched units or nothing, really.

Mixing wattage ratings in split-phase is basically asking two different-sized mates to carry a sofa — someone's getting a hernia and the sofa's going down the stairs anyway. 🛋️

@BatteryAlan the phase synchronisation alone will have Victron's engineers weeping into their stroopwafels — the VE.

@BatteryAlan following this closely — I've been planning my van build around a single Multiplus 12/3000 but have wondered about future expansion.

Genuine question though: even if you could get two mismatched units to handshake via VE.Bus, wouldn't the phase synchronisation become a nightmare under real load fluctuations? Like if one leg is pulling hard (say a compressor fridge kicking in) and the two inverters have different response curves, does that not risk the whole system going out of sync and dropping out?

Has anyone actually stress-tested this rather than just bench-tested it? I'd want to know what happens at 80%+ load on the smaller unit before committing to anything like this in a mobile setup where you can't exactly call an engineer out.

@BatteryAlan the fundamental issue is that Victron's split-phase implementation relies on precise phase synchronisation via the VE.Bus protocol — both units need to agree on timing and load sharing. Mismatched wattage ratings genuinely confuse this because the master/slave handshake assumes symmetrical capacity.

I ran a brief experiment on my narrowboat pairing a Multiplus 24/3000 with a 24/5000 — VEConfigure flagged warnings almost immediately and the system derated the larger unit to match the smaller one anyway. You lose the capacity advantage entirely.

Victron's own documentation (search "VE.Bus System Configurator" manual, page 34 ish) explicitly states matched VA ratings are required for parallel and split-phase operation.

Your realistic options:

• Match the units — sell your existing one and buy a pair
• Use a single larger unit and accept single-phase
• Look at Quattro pairing if input isolation matters

Don't fight the firmware on this one.